Circadian Stage-Dependent Inhibition of Human Breast Cancer Metabolism and Growth by the Nocturnal Melatonin Signal: Consequences of Its Disruption by Light at Night in Rats and Women

• Published in: Integrative cancer therapies Vol. 8; no. 4; pp. 347 - 353
• Main Authors: Blask, David E., Dauchy, Robert T., Brainard, George C., Hanifin, John P.
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA SAGE Publications 01.12.2009
• Subjects: Animals; Anticarcinogenic Agents - pharmacology; Breast Neoplasms - metabolism; Breast Neoplasms - pathology; Cell Growth Processes - drug effects; Cell Growth Processes - physiology; Cell Proliferation - drug effects; Circadian Rhythm - physiology; Female; Humans; Light; Linoleic Acid - metabolism; Linoleic Acids - metabolism; Melatonin - blood; Melatonin - pharmacology; Melatonin - physiology; Neoplasm Transplantation; Photoperiod; Rats; Rats, Nude; Receptors, Melatonin - physiology; Signal Transduction - drug effects; Transplantation, Heterologous; light at night; breast cancer; melatonin; circadian disruption; tumor metabolism
• ISSN: 1534-7354; 1552-695X; 1552-695X
• DOI: 10.1177/1534735409352320

The circadian production of melatonin by the pineal gland during the night provides an inhibitory signal to tissue-isolated steroid receptor SR+ and — MCF-7 human breast cancer xenografts in female nude rats. A pivotal mechanism for melatonin’s anticancer effects in vivo involves a melatonin receptor-mediated inhibition of linoleic acid (LA) uptake and its metabolism to mitogenically active 13-hydroxyoctadecadienoic acid (13-HODE). Exposure of (SR-) xenograft-bearing rats to increasing intensities of polychromatic white light at night suppresses melatonin while increasing tumor growth rates, DNA content, [3H]thymidine incorporation into DNA, LA uptake, 13-HODE formation, cAMP levels and ERK1/2 activation a dose-dependent manner. Similar effects occur in SR- human breast cancer xenografts perfused in situ with melatonin-depleted blood from healthy female subjects after their exposure to a single bright intensity (2800 lux) of polychromatic light at night. Additionally, SR- human breast cancer xenografts exhibit robust circadian rhythms of LA uptake, 13-HODE formation and proliferative activity. Exposure of xenograft-bearing rats to dim light at night results in the complete elimination of these rhythms which culminates in unfettered, high rates of tumor metabolism and growth. The organization of tumor metabolism and growth within circadian time structure by the oncostatic melatonin signal helps create a balance between the cancer and its host that is disrupted by host exposure to light at night. This biological mechanism may partially explain the higher risk of breast and other cancers in women working rotating night shifts and possibly others who also experience prolonged exposure to light at night.